As electronic systems are becoming more power efficient, fault tolerance to non-ideal loads and short circuit conditions have become more critical. Many circuits and systems include methods of detecting load fault conditions and mitigating their effects. For example, power driving devices contain output current sensors and monitors that will sense high current conditions brought about by short circuits or faulty loads, or low current conditions brought about by open circuits or other circuit faults. If a short circuit condition is detected, corrective measures can be such as shutting off the driver and/or reporting the fault to a controller.
Output current detection is relatively straightforward in situations where the load is being driven by a continuous signal or a low frequency signal, because the instantaneous output current at any particular time is usually an adequate indication of load conditions. In pulse modulated systems such as data communication systems and pulse width modulated power supply systems, however, the switching nature of the systems output creates some difficulty in load fault sensing.
In capacitively loaded systems, for example, the initial current drive at the onset of a pulse may be high enough to approximate short circuit or load fault conditions. In inductively loaded systems, on the other hand, the onset of a pulse may approximate an open load condition as the load inductance begins to conduct current. These systems are prone to false load fault detection if only simple current detection techniques are used.
One possible solution to this problem is to require the output current sensor to report a load fault condition over a predetermined period of time before recognizing a load fault condition. For example, in order for a load fault to be recognized, the output current detector must indicate a high current state or a low current state for a period of time that exceeds initial startup transients.
As pulse-width and pulse-code modulated systems are increasing in output frequency, however, requiring a detected current to be monitored over an extended period of time poses some difficulties. For example, if a pulse width is less than or on the order of a predetermined output fault detection time, an output fault will be inadequately detected. Consequently, higher power dissipated and possible system damage may result.
What are needed are systems and methods of fault detection for high frequency and/or narrow pulse-width switching systems.